Its blue, not black. And its always there.

The insignia is, technically, "4 blue 'M's arranged in a cross pattern and filled with yellow, often bordered in white and with a pre-war blue-yellow-red cockade in the center."
Often on those photos the blue used is light enough not to register seperate from the yellow of the cross, and sometimes it doesn't show on the rudder stripes either. Note thet there is very little contrast on the rudder of that photo.
Note the contrast in this photo of another 109...
And the complete lack of it in this almost identical aircraft.
Note the lack of contrast in this photo as well- the blue on the rudder actually shows up lighter than the neighboring yellow.
